In U.S. Patent Application Ser. No. 653,216 filed on Sept. 20 1984 by the present inventors and commonly owned herewith, there is described a vehicle suspension system comprising wheel suspension devices, the displacement of which can be varied, and means responsive to the loading of the suspension devices to feed back to the devices electric signals effecting a predetermined displacement. In European Patent Application No. 84 307 288.5 and in International Patent Application PCT/GB84/00358, both of which claim priority from UK Patent Application 83 28 373, there is disclosed a wheel suspension device for use in such a system and comprising an hydraulic actuator of which the piston position is adjustable in response to forces acting thereon and/or to a selected control input, and a load bearing strut responsive to the actuator piston experience to minimize the load carried by the actuator.
The system of U.S. Patent Application Ser. No. 653,216 offers substantial advantages over previous passive suspension systems, for example self-levelling of the vehicle under varying loads, due either to payload changes or to externally applied loads, can be effected. The system moreover has the ability to stabilize the vehicle under inertial loads such as braking, accelerating and cornering, so as to prevent changes in attitude of the vehicle. Additionally, the damping characteristics can be adaptively varied according to dynamic requirements of both the sprung and unsprung masses, to minimize transmitted accelerations, while maximizing the grip of the wheel on the road under varying conditions. Also, the system can be adapted to receive a selected energy input to further modify the damping characteristics.
The full advantages of such an active vehicle suspension system are obtained only by the input of considerable energy, and it is accordingly an object of the present invention to provide an active vehicle suspension system which reduces this energy demand under a wide range of conditions, for a given set of characteristics.